Flame ionization detectors have been used for a long time for measuring hydrocarbon concentration in automobile exhaust gases, as described, for example, in publication "Emission and Imission Measurement Technology in Traffic Systems", published by TUV Rheinland, 1993 printing, page 214.
The measurement principle of the flame ionization detector is based on the fact that ions are formed in a hydrogen flame from hydrocarbon molecules. The flame burns between two electrodes, to which a d.c. voltage is applied. The combustion air and the combustion gas (H.sub.2 or an H.sub.2 /He mixture) are introduced separately into the burner. The exhaust gas sample is mixed with the combustion gas in front of the burner nozzle. The ions formed by the flame produce a charge, which can be measured as an ion current.
The arrangement of the electrodes with their necessary insulation, screw connections and the like results in a complex mechanical construction which is relatively expensive and leads to high production costs. In addition, this arrangement of the electrodes is not suitable for a design having several channels, for example, for measuring overall hydrocarbon content and specific methane content in the automobile exhaust gas simultaneously.